Extrusion dies are frequently used to provide a tubular coating to a wire or other product which presents a generally cylindrical substrate. A typical die assembly 1 for performing this function is shown in FIG. 1. The basic assembly 1 consists of a die body 2, a tip 3, a die retainer 4, and a die 5. The tip 3 is mounted within an axial bore of the die body 2 and is itself constructed with an axial bore 7 having a downstream exit portion 8. In operation, a wire, or other tubular or profile product (not shown) is fed through bores 7 and 8 to exit axially at 15. An annular extrusion passage 9, surrounds exit 15, and is positioned to receive flowing plastic and apply it, in a tubular layer, to the product as it leaves exit 15. In some instances air may be blown through axial bore 7 to allow the formation of a hollow tubular part, accurate concentricity is still a critical requirement.
The die assembly 1 is an assembly of machined parts, each having its own manufacturing tolerance. These tolerances tend to multiply with the assembly of the components. It is therefore a difficult task to maintain the desired coaxial relationship between the product and the extruded layer to a particular tolerance. An adjustment mechanism is generally needed to insure concentricity of the die and pin, so as to provide an even thickness of the applied layer. This is generally accomplished simply by mounting the die retainer 4 for adjustment, along x and y coordinates (see FIG. 1a). The adjustment may be actuated through adjusting screws 12a, b, c, d. As shown in FIGS. 1a and 1b, the adjustment motion is radially towards and away from the axis 17, of the assembly 1. It should be noted that in the adjustment process of the prior art, as a torque is applied to an adjustment screw 12a, adjustment screw 12c must be backed off to allow movement of the die in the y direction. This also occurs when adjusting in the x direction. With this system of adjustment screws, the sensitivity of the adjustment mechanism is limited by the maximum thread density that can be machined.
It is a purpose of this invention to provide a simple mechanism for adjusting the relative position of the die with respect to the tip to apply a consistently concentric layer of plastic about the circumference of a tubular product, while reducing the torque required to adjust the position. Another purpose of the invention is to improve the accuracy of die adjustment in other die assemblies. It is another purpose of this invention to provide a module which incorporates the adjustment mechanism into an easily assembled component of the extrusion die assembly. A further object of the invention is to increase the sensitivity and accuracy of the concentricity adjustment.